In a thermal printer, such as is described in U.S. patent application Ser. No. 457,593 (filed Dec. 27, 1990, in the names of S. Sarraf, et al.), entitled "Thermal Printer", and assigned to the same assignee as the present patent application, a dye-donor element is placed in contact with a dye-receiving element onto which an image is to be printed. Then the donor element is irradiated by ultra-fine, focused spots of light from a laser. This operation applies heat to the donor element in the immediate vicinity of a light spot which heats the dye in the donor element to its vaporization temperature and transfers a small "dot" of dye to the surface of the receiver element. The laser light beam and its focused spot is scanned sequentially across the donor and receiver elements at high speed and with great accuracy and precision. While being scanned the laser light is modulated by electronic signals, which are representative of the shape, color, and detail of an image to be printed onto the receiver element. Successive dye-donor elements of different colors (e.g., cyan, magenta, and yellow) may be used to print full-color images on the receiver element. After the desired image has been transferred dot-by-dot from the donor element or elements onto the receiver element, it is necessary for the image to be permanently bonded or fused to the receiver element.
The image containing receiver element can be a slide transparency which is projected with enlargement (e.g., at 100 power magnification) onto a large screen. Seemingly minor distortions, or physical unevenness in the receiver element itself, or inaccuracy or non-uniform reproduction of an image, particularly a fine detail full-color image, are thus greatly magnified and can be visually objectionable. Thus there is a need for an extremely high degree of fidelity in the printed receiver image. This imposes stringent performance requirements on the mechanical, thermal and optical qualities of the receiver element itself, on the fidelity of the image printed on the receiver, and on the manufacturing process by which the receiver and image are bonded together.
It has been found to be advantageous, from the standpoint of high quality of the final product and for ease of operation in a thermal printer such as described above, to use individual molded plastic members as the dye-receiving elements when making slide transparencies. These plastic members can be produced as blanks in the exact shape and size of a standard transparency. They can then, without special handling or care in storage, be loaded into a magazine in the printer and used for printing one by one as required. Using the electronically controlled thermal printing process just described, a printer can, in a very short time and using an entirely "dry" process, print onto one of these plastic members a full-color, highly faithful reproduction of an image suitable for projection.
After an image, in the form of these small dots of dye (pixels) has been deposited by a thermal printer on the surface of a plastic receiver element, it is further necessary to bond or fuse the dots of dye to this surface so that they can not be rubbed off. The use of solvents or chemicals to bond the pixels of dye is undesirable because of fumes and for other considerations. On the other hand, thermal fusing or melt bonding the pixels of dye to the surface of the receiver element has proven difficult in the past because of many conflicting factors Using poorly controlled heat sources, such as a hot air blower or a coiled nichrome "toaster" wire, the results were not fully satisfactory because of resulting physical distortions caused by uneven heating of the receiver element. Uncontrolled heating also results in uneven or inadequate fusing of the dye pixels.
It is desirable to provide a fast, efficient apparatus for and method of heat fusing a dye-transfer image onto a plastic receiver element The end result is a low cost, rugged element (e.g., slide transparency) which has an image of high definition permanently fused to it without visual distortion or unevenness.